The present invention relates to RF phase shift devices, and more particularly to a device capable of producing a continuous, reciprocal, differential RF phase shift with a single control voltage.
Conventional phase shifters use either ferrites or PIN diodes to switch the phase characteristics of a transmission line. While recent developments in miniaturized, dual-toroid, ferrite phase shifters have allowed their integration into microstrip circuits to achieve reciprocal operation, PIN-diode phase shifters are still widely used. Depending on the particular application requirements, the digital phase bits are traditionally configured from one of the following circuit types: 1) switched line; 2) loaded line; 3) reflective (e.g., hybrid coupled); or 4) high-pass/low-pass filter.
A number of these circuits are typically connected in series to form a device that provides 360 degrees of differential phase shift. Circuit losses, along with parasitic elements of the PIN diodes and the bias networks required, increase the RF insertion loss above that of an equivalent, straight through, transmission line. Phase setting accuracy is limited to one-half of the smallest phase bit increment and results in phase quantization sidelobes that may be objectionable. Average power-handling capability is primarily limited by the maximum allowable temperature rise due to RF losses concentrated in the diode junction area. Cost, size, weight and reliability of the driver circuits and associated power supplies become important issues, as each phase bit requires a separate driver and control power for the PIN diodes can be substantial in a large array.
It is therefore an object of the present invention to provide an RF phase shift device that produces a continuous, reciprocal, differential RF phase shift with a single control voltage.